Superconductivity of MgB₂ composited with Mg-Zn alloys

The three-dimensional penetration method combined with semi-solid casting was used to fabricate metal-powder composite superconducting materials of MgB₂ with magnesium alloys: MgB₂/Mg - xwt% Zn (x =1,3, 6, 9). X-ray diffraction measurements indicated predominant peak patterns of MgB₂ and a host alloy. Measured electrical resistivity (ρ) versus temperature showed a clear signal of superconducting transition at about 34 K for all the samples cut out from the composites. External field (H) dependence of ρ(T,H) provided upper critical field of about 5 T. A volume fraction of the superconducting state of the sample estimated from a low external field part of magnetization was almost the same as the nominal ratio of MgB₂ powder against the host material. A magnetic hysteresis loop observed at 5 K suggested that an addition of Zn element to magnesium host-matrix little changed the critical current density (J_c). A comparison of the present results with the previous ones of MgB₂/Mg-Al-Zn systems confirmed that simultaneously doped Al and Zn were necessary to enhance J_c. Specific heat measurements of the sample with an external field showed that the bulk superconductivity of MgB₂ was well conserved in the composites.